1. Field of the Invention
The present invention relates generally to an electrical coaxial connector, and more particularly to an improvement in an electrical coaxial connector to be mounted on a circuit board for transmitting signals from the circuit board to the outside thereof under a condition of electro-magnetic shield.
2. Description of the Prior Art
A high-frequency signal flowing through conductors arranged on a circuit board is mostly dealt with as a signal which requires being put in a condition of electro-magnetic shield so as to be inactive to leak out from the conductors or to prevent noises from mixing thereinto from the outside. For transmitting the high-frequency signal on the circuit board to the outside thereof, for example, to another circuit board, under the condition of electro-magnetic shield, an electrical coaxial connector to be mounted on a circuit board is used.
Such an electrical coaxial connector comprises usually a signal-joining contacting conductor provided for transferring a signal and a grounding contacting conductor provided for surrounding the signal-joining contacting conductor to be supplied with a ground potential so as to put the signal supplied to the signal-joining contacting conductor in a condition of electro-magnetic shield. When the electrical coaxial connector is mounted on a circuit board to be used, the electrical coaxial connector is coupled with another electrical coaxial connector which is, for example, mounted on another circuit board, so that the signal-joining contacting conductor comes into contact with another signal-joining contacting conductor provided in the other electrical coaxial connector and the grounding contacting conductor comes into contact with another grounding contacting conductor provided in the other electrical coaxial connector. With the electrical coaxial connectors coupled with each other in such a manner, the signal supplied to one of the signal-joining contacting conductors is transferred to the other of the signal-joining contacting conductors under the condition of electro-magnetic shield brought about by the grounding contacting conductors. Thereby, the signal is transmitted between the circuit boards, on each of which the electrical coaxial connector is mounted, under the condition of electro-magnetic shield.
When the electrical coaxial connector as mentioned above is mounted on the circuit board, the signal-joining contacting conductor is connected to a signal terminal provided on the circuit board and the ground-connecting contacting conductor is connected to a ground-potential terminal provided on the circuit board. It is usual that a grounding terminal portion of the grounding contacting conductor is soldered to the ground-potential terminal provided on the circuit board so that the grounding contacting conductor is connected to the ground-potential terminal and a soldered condition of the grounding terminal portion of the grounding contacting conductor with the ground-potential terminal provided on the circuit board is required to be properly maintained for a relatively long period of time.
There has been proposed to provide an improved electrical coaxial connector in which a grounding contacting conductor has a distinctive grounding terminal portion which is provided to be soldered to a ground-potential terminal provided on a circuit board and so contrived in its shape that a soldered condition of the grounding terminal portion of the grounding contacting conductor with the ground-potential terminal provided on the circuit board is improved, as disclosed in, for example, the Japanese patent application published before examination under publication number 2004-63372.
The previously proposed electrical coaxial connector disclosed in the publication mentioned above comprises, for example, a signal-joining contacting conductor (contact) formed with a U-shaped conductive strip, a body made of insulator such as plastics or the like and provided to be put on a circuit board for holding the signal-joining contacting conductor at its central portion, and a grounding contacting conductor (shell) formed into a cylindrical shape for surrounding each of the body and the signal-joining contacting conductor held by the body to contain the same therein. When the body made of insulator is put on the circuit board, a contacting projection (signal terminal) provided on the signal-joining contacting conductor comes into contact with a signal terminal (pad) provided on the circuit board, so that the signal-joining contacting conductor formed into a U-shape is connected to the signal terminal provided on the circuit board. A plurality of grounding terminal portions (second ground-potential terminal) each formed into a plate shape are provided on a ring-shaped end of the grounding contacting conductor for coming into contact with ground-potential terminals (ground-potential pads) provided on the circuit board and soldered respectively to the ground-potential terminals provided on the circuit board, so that the grounding contacting conductor is connected to the ground-potential terminals on the circuit board.
Under such a situation, each of the grounding terminal portions provided on the ring-shaped end of the grounding contacting conductor is shaped to have chamfered edges or round-cornered so as to prevent the grounding terminal portions from being removed from the ground-potential terminals provided on the circuit board or to prevent the ground-potential terminals provided on the circuit board from being separated from the circuit board and thereby it is intended that the ground-potential is stabilized and each of the ground-potential terminals provided on the circuit board is strengthened in resistivity against separation from the circuit board.
In the above-mentioned previously proposed electrical coaxial connector in which the grounding terminal portions each formed into the plate shape and provided on the ring-shaped end of the grounding contacting conductor formed into the cylindrical shape are soldered respectively to the ground-potential terminals on the circuit board and thereby the grounding contacting conductor is connected to the ground-potential terminals on the circuit board, a soldered portion on the circuit board, at which the grounding terminal portion provided on the ring-shaped end of the grounding contacting conductor is soldered to the ground-potential terminals provided on the circuit board, receives undesirable stress exerted thereto so as to be feared to bring about troubles when the previously proposed electrical coaxial connector is coupled with another electrical coaxial connector with the signal-joining contacting conductor thereof coming into contact with another signal-joining contacting conductor provided in the other electrical coaxial connector and the grounding contacting conductor thereof coming into contact with another grounding contacting conductor provided in the other electrical coaxial connector.
That is, in the previously proposed electrical coaxial connector put in a condition wherein the signal-joining contacting conductor comes into contact with the other signal-joining contacting conductor provided in the other electrical coaxial connector and the grounding contacting conductor comes into contact with the other grounding contacting conductor provided in the other electrical coaxial connector, the grounding contacting conductor is resiliently transformed by engagement with the other grounding contacting conductor provided in the other electrical coaxial connector and operative to exert resilient force arising from its transformation to the other grounding contacting conductor provided in the other electrical coaxial connector and to lock the same when the grounding contacting conductor comes into contact with and then is in contact with the other grounding contacting conductor provided in the other electrical coaxial connector. Thereby, the stress arising from the transformation of the grounding contacting conductor is inflicted upon the soldered portion on the circuit board at which the grounding terminal portion provided on the ring-shaped end of the grounding contacting conductor is soldered to the ground-potential terminal provided on the circuit board.
As a result, with repetitions of the condition wherein the soldered portion on the circuit board at which the grounding terminal portion provided on the ring-shaped end of the grounding contacting conductor is soldered to the ground-potential terminals provided on the circuit board receives the undesirable stress exerted thereto, it is feared that cracks in solder, remove of the grounding terminal portion of the grounding contacting conductor form the ground-potential terminal on the circuit board, separation of the ground-potential terminal from the circuit board and so on are brought about on the soldered portion on the circuit board and thereby the soldered condition of the grounding terminal portion provided on the ring-shaped end of the grounding contacting conductor with the ground-potential terminal provided on the circuit board can not be properly maintained.